Electrical switching apparatus for automatic telephone-exchange systems



C. J. ERICKSON ELECTRICAL EWITCHING APPARATUS FOR AUTOMATIC TELEPHONE EXCHANGE SYSTEMS Filed Nov. 14 1905 15 sheets-Shet' 1 May 25, 1926. 1,586,033

J. ERICKSON ELECTRICAL SWITCHING APPARATUS FOR AUTOMATIC TELEPHONE EXCHANGE SYSTEMS Filed Nov. 14 1905 15 Sheets-Sheet 2 Wings 94s. I fizz/@ 222? May 25 1926.

C. J. ERICKSON ELECTRICAL SWITCHING APPARATUS FOR AUTOMATIC TELEPHONE EXCHANGE SYSTEMS 14 1905 13 she'ets-Shet 5 Filed Nov.

C. J. ERICKSON ELECTRICAL SWITCHING A APPARATUS FOR AUTOMATIC TELEPHONE EXCHANGE SYSTEMS Filed Nov. 14 1905 13 Sheets-Sheet 4 15 Sheets-Sheet 5 May 25 1926.

C- J. ERICKSON ELECTRICAL SWITCHING APPARATUS FOR AUTOMATIC TELEPHONE EXCHANGE SYSTEMS Filed Nov. 14

. May 25 1926.

,c; J. ERICKSON ELECTRICAL SWITCHING APPARATUS FOR AUTOMATIC TELEPHONE EXCHANGE SYSTEMS Fi-led Nov. 14 1905 13 Sheets-Sheet 6 May 25 1926. 1,586,033

6. J. ERICKSON ELECTRICAL SWITCHING APPARATUS FOR AUTOMATIC TELEPHONE EXCHANGE SYSTEMS Filed Nov. 14 1905 13 Sheets-Shetj May 25 1926. 1,586,033

C J. ERICKSON ELECTRICAL SWITCHING APPARATUS FOR AUTOMATIC TELEPHONE EXCHANGE SYSTEMS Filed Nov. 14 1905 1s Sheets-Sheet s May 25, 1926-.

C. J. ERICKSON ELECTRICAL SWITCHING APPARATUS FOR AUTOMATIC TELEPHONE EXCHANGE SYSTEMS Filed Nov. 14 1905 13 Sheets-Sheet 9 May 25 1926.

C. J. ERICKSON ELECTRICAL SWITCHING APPARATUS FOR AUTOMATIC TELEPHONE EXCHANGE SYSTEMS 13 Sheets-Sheet 1 Filed Nov. 14 1905 May 25 1926.

C. J. ERICKSON ELECTRICAL SWITCHING APPARATUS FOR AUTOMATIC TELEPHONE EXCHANGE SYSTEMS Filed Nov. 14 1905 13 Sheets-Sheet 1 1,586,033 C. J, ERICKSON ELECTRICAL SWITCHING APPARATUS FOR AUTOMATIC TELEPHONE EXCHANGE SYSTEMS Filed Nov. 14 1905 13 Shets-Shet 12 May 25 1926;

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C- J. ERICKSON ELECTRICAL SWITCHING APPARATUS FOR AUTOMATIC TELEPHONE EXCHANGE SYSTEMS Filed Nov. 14 1905 l3 Shets-Shet l 5 CHARLES J". ERICKSDN, Qlll CMCAGQ, ILLHQUIS, ASSIGNOR, BY MESNE ASSIGNMENTS, TO AUTOMATIQ ELECTRIC INCL, @JE CHICAG-Q, ILLINOIS, A CORPORATION 0F DELA- WARE.

ELECTRICAL SWITCHING APPAEATUS E'QE AUTOMATIC TELEPHGNE-EKGHGE fiYSTEMS.

hmillcation filed Elcvember M, M05. $eris1 No. ceases.

hoard operators-or at least to accomplish the operation of a certain proportion of the exchange or switchboard apparatus Without the assistance of switchboard operatorsand especially to automatic or semi-automatic telephone systems of that character in which "the subscribers are provided With switching means for transmiiting one or more electrical impulse, as hy momentarily grounding either one or both sides of the line-for operating one or more elcetrioallypropelled switching: machines at the exchange or cenll si on, In telephone ertchaho'e systems 0 Whether automatic or only a. is desirahle to pro de with a number of truiilol ass or other (307" lions which are common to all the 1b, s, or to al the members oi a "risers. For era.

o sid -"ahle also ided o groups o't oers each, and may he or y their each. go having trunk-line co oi' subscribershelohgs, or to which this group of subscribers s is quite large it may he accessory i'or each callin subscriber to selec from two or more i os' of trunk-lines before ohiaiii FU-OD. with the exchange to which the o o a r CQllllQc ion with the called subscribe-r e the called subscriber. In each case, of course, any idle trunk line in the first group will serve-the purposes of the calling subscriber, and this is true of the second and third groups, and of the fourth and fitth grou s, it the exchange is very large and inclu es a great number of subscribers, lo telephone systems of this character which are rery small, or which are of considerable size and operated only on a sens-automatic hesis, it may then become necessary for each calling subscriber to autoroaticaly select, only one trunk-line, or other similar connection, be fore the operation occurs by which the final connection is established directly with the called suhscrihers line; hut in any event and regardless of Whether the'eirchahge is large or small, or automatic or semi-automatic is character, it is desirable thee the central stetion or exchange apparatus he so Cfillsillfllfii'fiil and arranged that any calling sshscriher will necessarily and automatically select ct one idle r common CUZIlQCtlOIl before connection is ii sally established with. the line of the called subscriber; for with 1 i, the calling suhscrihe 4 ope ee in which i I the doc o connection or gets noicatihg we called suhscrih er 2; inc is busy. lo. 351, utemetic telephone system, the switching vchime Which picks out or selects ihe called suhscrihers lice and makes connection directly therewith is commohly li'iiorm as a connector; and iii the exchange is large enough to require it, these connectors are their arranged in groups and employed on aypercentage basis-that is to say, they can he divided iiito groups of ten, and each group of connectors can be allotted to a group oi? one hundred suhscrihers. ls. such case, it is desirable to provide other switching machines which are commonly known as selectors, and which are employed by calling subscribers in picking out idle trunk-lines, If the exchange is not very large, it "will only be necessary for each ill) Eli

calling; subscriber to use one selector connector in coneectiou with soy eslleol subscribers line; but it the exchange is lerger, it mey then. become necesssr'r y subscriber operste e first-selector then s secontl-selector anti finally s, coruoector before establishing connection with the celled subseribers line.

The first-selectors can each be sllotteol to e subscribers line, thus making the totsl number of first selectors equal to the total number of subscribers in the exchange then if second-selectors are uecesssis-11y these iutermediete selectors or switching machines can be employed on a percentage basis, thus for exzcoupe melting the total number secondselectors only onelenth of the total number of subscribers; end it will understeed that these selectors ere pretc'rabiy Lt. tliviuctl rite groups. in any event. a. s

lector is preferably e. switching nmclnue or v n 1 V such character than it can be coutiollecl b s N I N .4. L .f! the callu suoscii ct to the cm c or ccus it to pick out any usrticuisr group switchiug machines, either selectors or cones-e tors, the case may be, doing, escupcs momentarily of to calling subscriber roeticwly seal by i hing 2r" w w a; bi crcrlly cons select sin mean.)

of scribers Take for or gels syst which thereore only first-sclcctors connectors the a hange be- 'u t each size a capacity that second. snol s may be each allot-ted to a single subscriber s line, and the connectors may be arranged in groups and employed, upon a, basis ten per cent of the total number of subscribers, so that there rill be only onetenth as many connectors as the total number of subscribers lines entering the exchange. lVith. such arrangement any celling subscriber will first. operate his firstselector in such manner as to cause the same to url'iitrarily pick out the particular group of couuectors'in which the called subscribcrs line terminates; but after this and as it is immaterial which one of these connectors is employed, the selector momentarily escapes from the control of the calling subscriber and. proceeds automatically messes end. hi7

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the pm so of ing it to both selc -L sou moire connection with the exact or p g i r suhscrih line with W1 'ch concoction cl; l7 a connector, the cin creche cc of tote the the s plot ed an economical ero-entries .4 bot e selectors lllfl thc councc tols 3? ing co hen to the different SLY fibe s; Under such circumstances customurr to pl'OVlClQ such subscribcrs linc with is l1 4 l I u I divitlual switching device, and ti only ten first-selectors allotted to this group oi one hundred subscribers lines; and

it has been demonstrated t at these one huul3 naeaose dred individual-switches and ten first-selectors constitute a more economical and more satisfactory arrangement than the one hundred first-selectors which would, with the old arrangement, ordinarily be allotted to such a group of subscribers; for each individual switching device may obviously be very simple in construction and operation, inasmuch as it is never called upon to do anything but merel automatically select one of the ten first-he ectors, thus dispensing at this time with the operation which corresponds to the first portion of the operation of an ordinary selector, and practically reducing the whole operation of the individualswitch to a basis where it corresponds with only the second or automatic portion of the operation of a selector. Consequently, in systems employing individual switching machinery. the calling subscriber first automatically selects an idle tirsbselector, and then selects a second and even a third sclector, if the exchange is quite large, before finally and automatically selecting an idle connector, and before causing such cone motor to arbitrarily pick out and make connection with the particularline of the called subscriber; but,.'as stated, this arrangement has been found to be much more economical, and to give as good and even better results, than the old arrangement in which a regular first-selector is. provided for each subscriberscline. The current. for operating the switching machinery at the exchange is preferably supplied from a storage battery or other suitable centralized source of supply located at the central station, while the current for talking purposes may be supplied from local batteries or trom the said common source; and the current for ringing the bells at the subscribers stations is preferably supplied from an alternating-current dynamo or other suitable source at the eX-' change or central station; As explained, the subscribers are each provided with the switching devices for operating the switching machinery at the exchange or central station. In some cases, the arrangement is such that the calling subscriber in removing his receiver from the usual switch-hook automatically grounds one side of his line, and thereby brings about the transmission of an electrical impulse which operates the individual switching device. After this, the calling subscriber operates his calling device in such manner as to transmit the required number of impulses-that is to say, the impulses which represent the number of the called subscriber, and which bring about the operation of the switching machinery that results in the establishment of connection with the called subscribers line. When this has been done, the calling subscriber then presses a key or button, and this act results in a temporary transmission or supply of ringing-current to the called subscribers line, sufiicient to ring his bell. Many kinds of devices are. however, employed at the subscribersistations of automatic telephone exchanges for enabling the subscribers to themselves operate either all or a portion of the exchange apparatus or switching inachincry at the central station.

(Iienerally stated, the object of my invention is the provision of improved switching machinery which can be operated electrically over subscribers lines or other suitable linecircuits.

Special objects of my invention are the provision of an improved construction and arrangement whereby it is not necessary to provide each subscriber with a first-selcctor, but whereby to the contrary it is only necessary to provide a comparatively small number-say ten-first-selectors for a group of subscribers-say one hundred in number; the provision of an. improved construction and arrangement whereby each subscriber may be provided with a simple and comparatively inexpensive trunk-select ing switch mechanism, and whereby all of said subscribers individual-switches may be operated by a single switch-operating machine or mechanism which is common to all of the diti'crcnt subscribers in the group to which such individual-switches belong, and the said switch-operating machine and its associated group of subscribers individual switches constituting the means whereby any subscriber in the group may obtain co1p1ection with an idle first-selector or with any other switching device adapted for performing a trunking operation corresponding to the first digit of any called number; the provision of an improved construction and arrangement whereby a comparatively small number of outgoing trunk-lines-say ten can be allotted to a group of subscribers-say one hundred in numberand employed by them in calling other subscribers, and whereby each trunkline can be provided with a plurality of multiple terminals, one for each subscribers line in the group, and whereby connection betweenany subscribers line and trunk-line may be established by positively shifting the terminal of such trunk-line into engagement with a terminal of the calling subscribers line; the provision of an improved construction and arrangement wherey a group of trunk-lines may each be provided-with a plurality of movable and rigidly-connected multiple terminals, one for each subscribers line to which the group of trunklines is allotted, whereby connection between any particular trunk-line and any particular subscribers line may be established by simultaneously shifting all of the multiple contacts or terminals of such trunk-line in a certain direction. and in such manner that only one of such trunk-line-terminalsthe time, automatically set the terminal-bar cl till.

rality of multiple terminals for such trunkline, said terminals being distributed along .the length of their allotted bar, and each terminal being individual to a subscribers line, and whereby all of said trunk-line ten minal-bars ma be arranged parallel with each other an connected at one end with the switch-operating machine or mechanism which is common to all of the subscribers in the group; the provision of an improved construction and arrangement whereby any subscriber in calling and obtaining connection with an idle trunk-line will, at the same the next idle trunk-line in position to be released for the purpose of effecting the connection between its trunk-line and the line of the subscriber making the next call; the provision of an improved construction and arrangement whereby the multiple terminals of the idle trunk-line next in order after the trunk-line last put in use are always held in readiness to bereleased and caused to shift in such direction as to complete a connection between their allotted trunk-line and the line of the subscriber making the next call; the provision of an improved construction and arrangement whereby all of the switch-contacts and other parts which are individual to a subscriber-that is to say, which are comprised in a subscribers individual trunk-selecting switch mechanismare not in any-way subject to actuation or disturbance by other subscribers, with the one exception of the trunk-line-terminals which are individual to any such subscriber; the provision of an improved construction and arrangement involving movable trunklinerterminals, and whereby each subscriber in making a call not only automatically obtains connection with the previously selected idletrunk-line, but also at the same time automatically sets allot the subscribers individual switch mechanisms in selective relation to the next idle trunk-line; and the provision of certain details and features of improvement tending to increase the general eliiciency and serviceability of electrical apparatus and devices of this particular character.

To the foregoing and other useful ends, my invention consists in matters hereinafter set forth and claimed.

In the accompanying drawings, Fig. 1'

is a full-sized plan view of one end of my improved individual-switch apparatus,

mechanism by which the longitudinallyshifting trunk-line terminal-bars are actu ated.

Fig.- 2 is a plan view of the other end of the said apparatus-that is to say, the end at which the trunk-lines are attached to their respective terminal-bars.

Fig. 3 is a side elevation of the mechanism shown in Fig. 1, and showing in addition four of the subscribers movable line-terminals.

Figs. 3 and 3* are detail views illustrating the switch-s rings and actuating-finger therefor operate by the propelling or power magnet of the switch-operating machine.

'Fig. is a cross-section on line 4' 1 in Fig; i.

, ig: 5 shows the mechanism shown in the right hand halt of Fig. 4, and shows the an scribers line-relay energized.

Fig. 6 is a detail sectional view showing the normal position of the subscribers movable line-terminals.

Fig. 7 is a view similar to Fig. 6, but shows the subscribers movable line-terminal in connective relation to one of the multiple terminals of one of the trunk-line tcrminah bars. 7

Fig. 8 is a longitudinal section on line 8-ci in Fig. i.

Fig. 9 is a iiragmentary perspective view of the ends of several of the trunk-line terminal-bars, and of the adjacent devices for actuating and controlling the operation of said bars:

Fig. 10 is a detail view of one oi? the cirwit-controlling devices.

Fig. 11 is a fragmentary perspective view illustrating the circuit-controlling device shown in Fig. 10.

Fig. 12 is a detail perspective view illustrating a part of the means for bringing a subscribers movable lineterminal into connective position.

Fig. 13 is a view similar to Fig. 12, except that it shows the manner in which a spring finger carried by the subscribers lineterminal is caught and held by a spring finger carried by a longitudinally-shifting bar operated by the switch-operating machine.v

Fig. 14 is a detail perspective view showing one of the multiple line-terininals of a subscribers line' in contact with one of the multiple terminals of a trunk-line, and showing another multiple terminal of the same subscribers line out of engagement with one of the multiple-terminals of another trunk-line.

Fig. 15 is a detail of the relays which are scriber s line, and showing two. of the lower ion llil

Ill

' nceaoea relays which are also eachindividual to one of said subscribers lines, one upper and one lower relay bein allotted .to each line.

Fig. 17 is a etail view illustrating the circuit controlling devices which are operated by the tops or upper ends of the subscribers swinging line-terminal banks.

Fig. 18 is a detail perspective of meet the circuit-closing devices shown in Fig. 17. Figs. 19 to 25, inclusive, are detail views illustrating different parts of the switchoperatiing machine-that is, the operating connections between the trunk-line terminalbars and the means for actuating the same.

Fi 26 is a simplified diagram illustrating t e subscribers individual apparatus and tracing, in dark lines, the line-circuit from a subscribers line through the individualswitch mechanism, and over the temporarily connected trunk-line to a first-selector.

Fig. 27 is a simplified diagrammatic view illustrating the line and auxiliary circuits formed by the'calling subscriber in getting connection with a"connector, and with a terminal of the called snbscribers line.-

Fig. 28 illustrates the called subscribers line and auxiliary circuits, and also the called subscribers individual trunk-selecting switch mechanism, it being observed that this diagram'and that shown in Fig. 27 really constitute one complete diagram of the connections between a calling and called subscribers stations. Fig. 29 is a combined perspective and diarammatic view of the firstselector shown in Figs. 26 and 27. Fl 30 is a similar view of the connec tor indicated in Fig. 27. V

As thus illustrated, it will be seen that my improved trunk-selecting switch mechanism comprises a plurality of trunk-line terminal-bars 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. These bars are preferably arranged in parallel relation to each other, and in a horizontal position, as shown in Fi 4. Each bar represents a trunk-line, an there are, therefore, as many trunk-line terminal-bars as there are trunk-lines allotted to the group of subscribers represented by the trunk selecting switch mechanism. as a whole. For example, there may be one hundred subscribers in each group and for each oup there will then be ten trunk-lines to used in common by the subscribers in the group in calling other subscribers. As shown, the said trunk-"line terminal-bars are supported in a bed or frame composed of parallel angleirons 11 and 12 which are connected by bars or cross-pieces 13. Preferably, each bar has its lower surface provided with a lon itudinally-extending r1b 14, and these ri s are adapted to slide longitudinally in notches or grooves provided in the upper surfaces of the cross-bars 13. it will be seen that the construction is such that the fiat lower sun faces of the trunk-line terminal-bars are adapted to rest and slide smoothly upon the upper surfaces of the cross-bars 13. With this arrangement, the bars are held close together between the inner surfaces of the channel-irons 11 and 12, but are maintained just far enough apart to prevent undue friction. It will be understood that in accordancewith the general scheme of in invention, these bars are preferably adapted for endwise I pendently of the others, and for the purpose of eflecting the automatic selection of idle trunk-lines, as well. as the connection of the next idle trunk-line with the subscriber making the next call. Each of said longitudinally-shifting bars is composed of longitudinally-extending strips of conducting metal, such as brass, with interposed strips of insulation, such as rubber vulcanite. As shown, the said ribs 14 do not necessarily extend for the full length of the different bars, and are only provided for a short distance each side of the cross-bars 13, inasmuch as the said trunk-line terminalhars are not engaged or supported in any way at points between these cross-bars 13. It will also be seen that each bar consists of two outside metal plates or side portions, together with three intermediate metal strips, all of said metal strips being insulated from each other by interposed strips of suitable insulation. In each trunk-line terminal-bar two of the intermediate metal strips are voice-current conductors, being connected with the so-called vertical and rotary line-conductors of the trunk-line allotted to the bar, while the third intermediate metal strip in each bar has various functions, as will hereinafter more fully appear. For example, in the terminal-bar 10 there are two outside metal strips 15, and three intermediate metal stri s 16, 17 and 18, all of said metal strips sing secured together by transverse clamping-screws 19 (see Fig. 8) and insulated from each other by longitudinal strips of insulation. At

the rear end of the bar 10 these intermediate metal conducting-strips are provided with terminals or attaching portions 20, 21 and 22. The terminals21 and 22 are attached, respectively, to the so-called vertical and rotary line-conductors of thetrunkline running to a first-selector or other switching apparatus, while the terminal or attaching portion 20 is attached to the third trunk-line-conductor running to the same first-selector or other suitable switching shifting movement, each indemeans. In this way, each trunk-line terrninal-bar is connected with three trunk-line conductors running to a selector, there being, therefore, as many first-selectors as there are trunk line terminal-bars in the subscribers automatic trunk-selectin apparatus comprising such hars. Distri uted Edit lti

at regular intervals along their lengths, eech terminal-bur is provided with as many multiple trnnk-line-terminuls as there are subscribers in the particular group to which the bars as a whole are allotted. For example, if there are one hundred subscribers in the group, the said trunk-line terminalburs will then he of considerable length, and each bar will be provided with one hundred trunlclineterininals which are, of course, connected in multiple and distributed at regular intervals along the length of such bar. lhese multiple trunk-lineterminals; with which the trunlnline terminal-bars ere provided consist, preferably, of small pro iections or switcl'i-cuntacts located upon the upper edges of the intermediate or conducting metal strips of the szud burs. For exemple, and referring more particularly lli 's. 1 end 4%, will be seen that the termins -ber 10 has its to "ward end portion provided with set oi contacts 23, 24: and 25,

' the same being formed integral. with the upper edges ot the metal strips 1-6, 1'? and 18, respectively. These contacts 23, 24- and 25 are individual to a single subscriber, end are arranged in a row extending obliquely across the bar 10, thus bringing each con tsct at it different point in the length of such bur. Further along, the suid her 10 is provided with e similar set of contacts 2 27 and 28, which are formed integral with the motel strips ill, 17 end 18, respectively,end which constitute a multiple trunk-line-teriuinul which is individual to another subscriber. At a oint further along, the seid bar 10 is provi ed with 2 similar set of contsctsfllil, 30 end ill constituting s third multiple trunk-linederminel which is individual third subscriber. in this way, each be. us expleined, provided on its uppersurlece with a plurality of smell projections or switch-contacts, each set constituting a trunk-line-terminel which is individual to single subscriber, and all of the different trunlr-line-terminels thus distributed along the length of e terminahbur being connected, of course, in multiple. 'With the construction shown end described, the multiple trunloline-terminels of any articular trunk line are not only electrics 1y connected in multiple, but are alsov mechanically and rigidly connected together, whereby all of the multiple trunlr-line-terminuls of any particular trunkdine may be shifted in unison. Referring again to Fig. 1, it will be seen that all of the other trunk-line terminslbsrsnre provided on their upper surfaces with sets of contacts similar to those just described in connection with the bar 10, each terminal-bar being provided with a trunk-line-te rminal which is individual to one'of the subscribers of the group. With this arrangement it will be seen that the practically smooti or flushupper surface essence composed of the upper surfaces ot the different terminalbars is provided with ten times as many trunlr-line-terminuls as there are subscribers in the group, these trunklin e-terminels being crranged in rows both longitudinally and trensversely of the group of terminel-bsrs. All of the trunk-line-terminuls which are allotted to a single trunkline, but which ere each individual to a dif- :lerent subscriliers line, are distributed ulong the length of a single. terminal-bur. lit will he seen, however, that all of the trunlr-line-terminuls which sre'individuel to the sums subscrihers line, but which are each individual to e diliferent trunk-line, ere

srrenged in e row extending transversely .ecross the upper surince of the group oi terminal-bars. In this way, there are ellotted to such subscribers line as many trunk-line-terminels us there are trunk-lines for the group, thus giving each subscriber in the group n haul: of trunk-line-terminuls each connected with a ditlerent trunk-line; but with my improved arrangement, the trunlnlineterminals oi any given subscribers bunk ere each movable independently of the others, and each connected both electrically and mechanically with oil of its multiple trunk-lineterminels; end with this errengement, the shifting of e trunk-lineterminul'in any particular subscribefls banlr necesserily results in 9, simultaneous and corresponding movement on the part of all of the multiples of such terminal which are distrihuted through the hunks of the other subscribers. lit will be seen, therefore, that each of the transverse rows of trunk-lineterminuls, extending across the group of terminuhhers, is individual to at single subscriber, each of said rows constituting a bunk of trunlr-line-terminnls each connected with e dillerent trunk-line. Furthermore, with this arrangement, each subscribers line is provided with s bunk of swinging end endwise-niovehle multiple line-terminals, 'euch subscribers bank oi line-terminals associated with the corresponding bank of trunk-lineterminsls. in other words, in the trunln selecting mechanism which is individual to e single subscriber there are included a bank of trunlt-line-terininals each of which is connected with a diii erent trunk-line, and at bank of subscribers line-terminals each of which is connected with the subscribers line, the two banks being arranged opposite each other and edapted to cooperate with ouch other in establishing connection between the subscriloers line and any one of the dillerent trunk-lines. Consequently, the bank of subscribers line-terminals of any individual switch is composed of terminals which are all multiples of the same subscribers line, while the bank of trunk-line-terminals 'of the some individual-switch is composed of terminals which are all multiples of dif ill nesaose ferent trunk-lines. In other words, each subscribers line-terminal being arranged to lit) cooperate exclusively with a certain trunkline-terminal. For example, and referring more particularly to Figs. 2, 3 and '4, it Wlll be seen that the subscriber to whom is allotted the bank of trunk-line-terminals including the contacts 23, 24 and 25 is provided with a bank 32 of swinging and endwisemovable line-contacts arranged directly over the said transverse bank of trunk-line-terminals. This bank 32 is provided at one end with a pin 33 adapted to extend through an opening in the upright spring post 34, which latter is secured to the outside of the angle iron 11. At its other end, the said bank 32 is provided with a similar pin or trunnion 35 adapted to extend through an opening in the rigid or non-swinging upright 36, which latter is secured to the outside of the angle-iron 12. The said bank 32 is, it will be seen, composed of a front plate 37 held in electrical contact with a thin metal plate provided with downwardly-extending spring fingers or contacts 38, 39, 40, 41, 42, 43, 44, 45, 4-6 and47. The said front plate 37 is provided with a downwardly-extending arm 48 provided at its lower end with a notch 49.

A relatively thick bar or metal strip 50 is separated and insulated from the strip havin the teeth 38, 39, etc., by a strip of insu ation 51. Another plate 52, similarto the plate 37 is insulated from the strip 50 by insulation 53. A thin sheet-metal strip is maintained in electrical contact with the plate 52, and is provided with spring fingers or contacts 54, 55, 56, 57, 5s, 59, 50, e1, 62 and 63. It will be observed that these spring fingers or downwardly-extending electrical contacts are, as a whole, shifted slightly to one side, so that they are out of line with A the spring fingers 38 to' 47, inclusive. metal late 64 is separated and insulated from tli strip having the fingers 54 to 63, inclusive, by a strip of insulation 65. A third strip of sheet-metal having a third setof sprin fingers 66 to 75, inclusive, is held in electr cal contact with the late 64. The back clamping-strip 76 is insu ated from the spring fingers 66 to 75, inclusive, by a strip of insulation 77. The superimposed strips of metal and insulation thus provided are bound together by clamping-screws 78, each of which is referably provided with a sleeve of insu ation 79. In this way, the three conducting-plates of the subscribers bank of line-contacts or multiple terminals are rigidly connected but thoroughly insulated from each other. The intermediate bar or metal strip 50 has its ends provided with the said pins or trunnions 33' and 35 previously referred to. Preferably, the plates 37 and 52 are provided, respectively,

tor of the said subscribers line.

with circuit-controlling contacts 80 and'81 adapted to cooperate with the stationary 1 contacts 82 and 83, which latter are insulated from each other and suitably mounted upon a bar or mounting-stri 84 extending longitudinally of the switching machine and just above all of the difierent subscribers lineterminal banks (see Figs. 17 and 18). This longitudinally-extending bar or mounting 84 can be supported by transverse bridging bars 85 arranged at suitable intervals along the length of the machine, and in such man- I ner as to extend across the longitudinally reciprocating trunk-lme terminal-bars. It

will also be seen that the three sets of spring fingers or contacts, namely, 38 to 47, inclusiv, and 54 to 63, inclusive, and 66 to 75,

inclusive, are provided, respectively, with terminals 86, 87 and 88 to which are secured wires or other flexible conductors. The fingers or contacts of the first set are privatecontacts, so to speak, and are never included in any talking-circuit, but are simply used for establishing a guarding potential, etc., as will hereinafter more fully appear. The

second and third sets of s ring fingers or contacts, namely, 54 to 63, lnclusive, and 66 to 75, inclusive, are talking-contacts-that is to say, switch-contacts adapted to be included in talking-circuits for conducting the voice-currents from one subscribers station to another. The second or intermediate set of spring fingers or contacts (54 to 63, inclusive) consists of ten spring fingers connected in multiple, and all connected with the so-called vertical-line-conductor of the subscribers line to whom the bank is allotted. The outside or third set of spring fingers (66 to 75, inclusive) consists of ten spring fingers or contacts which are connected in multiple, and which are allconnected with the so-called rotary line-conduc- Thus each subscribers endwise-shiftable and oscillating bank of line-contacts (the bank of multiple contacts which is connected with and individual to the subscribers line) is composed of ten sets of contacts, each set constituting a multiple line-terminal. For example, the subscribers line-bank 32 has ten sets of contacts, and these ten sets are connected together in such manner as to provide ten multi le line-terminals, each set or terminal inclu ing its allotted private-contact or terminalthat is to say, each terminal or set of contacts comprises two line-contacts which are used for transmitting the voicecurrents, and a third contact which is employed as a private-contact in establishing a guarding potential for energizing certain relays, etc. Each subscribers bank of multiple line-terminals comprises, therefore. ten so-called vertical-line-contacts arranged in a row and connected in multiple; a similar row of so-called rotary-line-contacts ,con- 

